1. Empty toilet paper rolls

Wipe away that look of disbelief. Empty toilet paper rolls can be turned into cold hard cash. Used for all sorts of school and craft projects, 200 of these cardboard cylinders will fetch about $35.00 on eBay.

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2. Four-leaf clovers

Searching for four leaf clovers is a great way to help kids unplug and enjoy the great outdoors. Each one of these dry pressed lucky charms sells for about $6.00 on eBay. Not bad for an afternoon spent lounging in the warm summer breeze.

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3. Paper currency

Sure, cash isn't technically free, but certain bills can be worth far more than their face value. Check your wallet and piggy bank; modern bills that feature distinctive (collectors call them "fancy") serial number combinations can bring big bucks.

Look for large groups of the same digit, repeating sets of digits, sequential digits, and very low or very high numbers. Last week, a 2009 one dollar bill sold for $11.00 on eBay. Its eight-digit serial number was 18611111. In April, a 2013 one dollar bill with the low serial number of 00001004 brought $30.00.

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4. Sea glass

Crafters and jewelers are drawn to the subtle beauty of surf-tumbled sea glass. While all colors sell, deep purple, orange, and red glass are the rarest and most highly prized. Recently, a single piece of ruby red sea glass (part of an old soda bottle bottom worn smooth from years in the ocean) sold for $99.00 on eBay.

5. Driftwood

Large sculptural pieces of driftwood are used in landscaping, terrarium design, professional taxidermy projects, and as decorative elements in aquariums. Simple forms can fetch $10.00, while more interesting shapes can bring as much as $85.00. But don't ignore the tiny bits of driftwood. Smaller 2"-10" twigs can be sold in bulk to crafters for all sorts of projects. A 14-piece lot recently sold on eBay for $15.00.

Remember, before gathering driftwood on public land, check with local park officials. Many areas have restrictions that forbid the removal of any natural materials.

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6. Large pine cones

Believe it or not, pine cones can be a modest cash crop. Particularly hot around the holiday season, they're a staple in home décor, flower-arranging, wreath-making, and other craft projects. A lot of 40 longleaf pine cones recently sold on eBay for $18.99. Hmm… maybe money doesgrow on trees.

7. Empty perfume bottles

Perfume bottles are charming vessels for floral centerpieces at weddings and bridal showers. Don't worry about the rarity, size, shape, or color. In March, a collection of 15 miniature perfume bottles sold for $39.99 on eBay.

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8. Perfume, makeup, and skin-care product samples

Samples appeal to customers who want a low cost way to try something new or who are simply looking for more travel-friendly sizes of their favorite products. If you have samples to sell, be thorough in your listing. Specify the product amount in ounces or grams, its age, and the expiration date. Sixteen free samples of Dermalogica Gentle Cream Exfoliant recently sold on eBay for $10.00.

Remember, the key to successful online selling is research. Take a look at what's selling and what's not, explore niche markets, try to anticipate what people will be clamoring for during the next big holiday season, and — before you toss it out — check to see what it might be worth!